University of Twente Student Theses


Spatio-Temporal Groundwater Recharge Assessment Serowe case study, Botswana

Setimela, Kenneth (2009) Spatio-Temporal Groundwater Recharge Assessment Serowe case study, Botswana.

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Abstract:Recharge quantification and assessment is vey vital for the management of aquifer and well fields. A number of recharge methods are available and applicable for different environments. Groundwater recharge in arid and semi-arid environments like Serowe is very erratic due to the unreliable and low rainfall. Two methods of groundwater recharge assessment were employed to assess the spatial and temporal variability of groundwater recharge of the Serowe aquifer: the chloride mass balance (CMB) method and the pyEARTH-1D model. CMB method was used to assess the spatial variability of the groundwater recharge using GIS interpolation techniques. Net groundwater recharge determined by CMB method showed generally high values to the east of the escarpment and at topographically high areas in the vicinity of the escarpment. Recharge is generally low in the sandveld part of the study area. Some areas that are affected by fracturing also exhibit relatively high recharge aided by preferential flow of water through these fractures. The pyEARTH-1D model that computes daily recharge based on deterministic methods that simulate soil physical processes, was used to determine the temporal variability of net groundwater recharge. The input driving forces, which are daily rainfall (P) and potential evapotranspiration (PET), were considered homogeneous over the study area, since the correlation between the 9 micrometeorological stations is high. Thus reference evapotranspiration (ETo) and P for the study area were acquired and processed only at the Malebala station (GS10). Besides a moderate correlation due to relatively high distance, the time series were completed by correlating data from GS10 with data from the NOAANCDC Mahalalpye meteorological station. ETo for GS10 was calculated by the FAO Penma-Monteith method while the ETo for Mahalalpye station was calculated by Hargreaves equation. ETo and P are temporally variable but less spatial variable. pyEARTH-1D model was applied at 7 locations scattered over the area and representing different hydrogeological settings between September 2001 and October 2008. Results show that the total recharge amount varies spatially (higher in the hardveld and lower in the sandveld). Groundwater levels analysis of the area show very little variability, but delayed aquifer recharge. The recharge of the aquifer as calculated by CMB ranges from 2.9% to 4.1% while that calculated by pyEARTH-1D model ranges from 1 to 6 %. The results show a good agreement between CMB method and pyEARTH-1D. There is a noticeable general decline in groundwater levels probably due to interference by production wells pumping. This should be cross-checked with borehole abstraction data and inserted in a fully transient model. This would be a very efficient tool for water management and understanding of natural (dynamic) fluctuations and interactions with human abstractions.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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